I'm currently working on a reasonably new Toyota Landcruiser which is suffering from a bad vibration that can be felt through the steering wheel. The vehicle in question is fitted with a Diesel V8 engine and automatic transmission.

Using the Picoscope with the Pico NVH kit, I was able to determine that the vibration was of the fourth order. When the vibration is the most severe (engine RPM approx. 1980Rpm) the vibrations being transmitted to the base of steering column can be in the vicinity of 30mg in amplitude. Understanding that a E4 vibration is normal for a V8 engine vehicle, I started to look for a reason for the vibration being excessive at the steering wheel.

Even with the engine idling, with the A/C cycling engine RPM from 600 to 800 RPM, I'm picking up an increase of 26mg at the steering wheel (NVH accelerometer held against the steering wheel)

The question is - why have I got so much vibration being transmitted to the steering wheel?

I managed to get a comparable vehicle to check vibration values between the two vehicles.The comparison vehicle has the same Body, Engine, Transmission, etc - but is a lower grade (plastic coated steering wheel as opposed to the leather / wood grain steering wheel of the luxury subject vehicle)

After measuring the E4 vibration at multiple locations (Engine, LH chassis, RH chassis, Steering shaft engine side and steering wheel side, LH and RH steering rack ends and of course - at the steering wheel itself) I have come to the conclusion that my diagnosis of the transmission path of the vibration is inconclusive!

That being said - I have really only done a static comparison between the two vehicles. I figure that would be ok as the ability for the Picoscope to pick up the smallest levels of the vibration would still show varying levels of the vibration - but the severity would increase when the engine was driven and put under load.

Below is the measurements taken from the comparison vehicle and subject vehicle.Both vehicles had reached operating temperature and were left to idle with the air conditioning left on for RPM variation.

My question is - Am I even heading in the right direction in terms of gathering information that will help lead me to the cause of the vibration being felt so badly in the steering wheel of the subject vehicle?

Would there be a simpler, more direct way to chase down the path that this 'normal' vibration is being transferred along?

However all 3 axis are summed together inside the single output NVH interface box in such way as to give the end user an overview (average) of all 3 axis . Here then there is no rejection of a particular vibration in a specific axis/direction, everything is accounted for.

Only the average vibration can be displayed, therefore we cannot identify the offending vibrations resultant effect upon the vehicle. We do not know if the resultant vibration is Fore/Aft, Vertical or Lateral

Using the 3 axis “average” principle it is very time consuming to identify the transfer path of a vibration as we cannot easily identify the direction of vibration (axis responsible)

With all that said we can still trace down this vibration and your test results are most helpful.

My first concern is the “back to back” test as you mentioned the style of steering wheel. The Leather and wooden steering wheel may well be applicable to Landcruisers with VGRS (Variable Gear Ratio Steering) and so the steering column and link assembly may differ drastically between your Landcruisers. Could you confirm this is not the case?

Do you or any colleagues in other Toyota centres have access to an identical Landcruiser with the luxury steering wheel option?

Could they take a vibration measurement for you?

If the steering column is the antenna for the vibration the mass at the end of the column (steering wheel) will have an adverse effect on how much vibration is experienced by the driver.

Additional mass is used to “shift” the resonance point of vibrations in order to remove them from normal operating conditions.

Forgive me here (as you may have already tried this) can we interchange steering wheels and retest the symptom?

Coming back to your test results: Subject Vehicle

We have an increased engine vibration on the subject vehicle at 800 rpm

To summarise these results, the vibration levels are clearly higher on the RH side of this RHD vehicle.

You are most certainly heading in the right direction.

In all of this diagnosis, we must not forget the source of vibration which is the engine.

Can we confirm the engine to be running correctly with even injector feedback values (Even Combustion?) Can we confirm fuel lines, fuel pipes, wiring harness, A/C pipes and control cables etc. that connect components mounted on the chassis to the engine are all mounted correctly with no “foul” conditions.

With regards to “Would there be a simpler, more direct way to chase down the path that this 'normal' vibration is being transferred along?”

This is where the 3 output NVH interface and software would help as you then have multiple accelerometer options at your disposal allowing you to plot vibration levels around the chassis and steering column.

Never the less you still have good diagnostic capability with the NVH kit you have.

We know the vibration is higher on the RH side of the vehicle

We have a donor vehicle for comparison

We can interchange steering wheel or add weight/mass to the luxury steering wheel to compare effect.